1. Field of the Invention
This invention relates to electronic engine controls and electronic diagnostics for an internal combustion engine.
2. Prior Art
U.S. Pat. No. 5,099,680 teaches an onboard system for analyzing exhaust gas emissions using a non-dispersive infrared gas analyzer system such as disclosed in U.S. Pat. No. 5,060,505.
Non-dispersive Infrared (IR) gas analyzers utilize an IR source to direct IR radiation though a mixture of gases contained in a sample chamber. The IR energy is passed through the mixture in the sample chamber at absorption frequencies for gases whose concentration is to be determined. The detected absorption at each frequency is indicative of the concentration of the component gas having the particular absorption band. In the particular application to automotive gas analyzers, the gases whose concentrations are of interest include HC (hydrocarbons), CO and CO.sub.2. In order to measure the concentration of these gases, multiple light filters, having transmission bands at an absorption band for each component gas, are alternatingly placed between the source and detector to provide an indication for each gas. The detector output is a single, time-multiplexed signal which contains information for all component gas concentrations. This signal is conventionally demultiplexed into individual signals and applied to separate amplifier channels for each gas component.
Thus, it is known to make measurements, mostly non-dispersive infrared absorption measurements, in a traditional and well controlled fashion in order to obtain precise and accurate assessments of exhaust gas components. However, such methods require samples that are external to the vehicle, i.e., after exiting the exhaust pipe or after removal of a portion of the tail pipe flow.
It would be desirable to be able to measure the exhaust composition in a less controlled environment at the face of a catalyst coupled to the exhaust flow from an internal combustion engine. In particular, it would be desirable to make this measurement either before and/or after passage through the catalyst.
Also known are oxygen sensors coupled to the exhaust stream. However, such sensors are limited to sensing oxygen. It would be desirable to have a sensor which could sense any of a variety of species other than oxygen, i.e., carbon dioxide, carbon monoxide, oxides of nitrogen, water and hydrocarbons. This invention provides such advantages.